Field of the Invention
This invention relates to the use of water soluble, low molecular weight copolymers of acrylic acid to disperse inorganic particulate matter and to inhibit the precipitation of common hardness ion salts in aqueous systems. More particularly, the invention relates to the use of certain copolymers, having a weight average molecular weight of from about 2,000 to about 5,000 formed from about 85 weight percent to about 97 weight percent acrylic acid monomer and from about 3 weight percent to about 15 weight percent of a hydrophobic monomer, to disperse suspended inorganic particulate matter and to inhibit the precipitation of hardness ion salts in aqueous systems.
Much of the water used in recirculating cooling water systems and water cooled industrial heat exchangers supplied from rivers, lakes, ponds and the like contains high concentrations of suspended inorganic particulate materials such as mud, silt and clay. In cooling tower systems, the cooling effect is achieved by evaporating a portion of the water circulating through the tower. This evaporating results in the concentration of the suspended materials in the water. These materials settle in locations of low flow rates and cause corrosion, frictional losses and inefficient heat transfer.
Water used in cooling systems and water-cooled heat exchangers also contains dissolved salts of hardness ions, such as calcium and magnesium. These salts can precipitate from solution and lead to the formation of scale on the heating surfaces of the cooling systems or exchangers. The most common deposit found in cooling water systems is calcium carbonate. Calcium carbonate has a relatively low solubility in water. This solubility decreases with increasing pH, temperature and concentration. Calcium sulfate is also likely to be encountered in cooling water systems. Calcium sulfate may result from the addition of sulfuric acid to raw water to control calcium carbonate scale. While calcium sulfate is more soluble than calcium carbonate, the solubility limit of calcium sulfate can also be easily exceeded resulting in its precipitation from solution.
High molecular weight polyacrylates and polyacrylamides have been used to agglomerate fine particles of mud and silt into a loose floc to reduce the accumulation of these materials in pipes and heat exchanger tubes. However, these flocs tend to settle in cooling tower basins which then require frequent cleaning for their removal.
Many other compounds have been developed and are being used with varying degrees of success to disperse suspended particulate matter and to inhibit the precipitation of hardness ion salts and the resultant formation of scale in aqueous systems.